Device comprising a fluid channel fitted with at least one microelectronic or nanoelectronic system, and method for manufacturing such a device

ABSTRACT

A device comprising a substrate comprising at least one microelectronic and/or nanoelectronic structure comprising at least one sensitive portion and one fluid channel ( 2 ) defined between said substrate and a cap ( 6 ), where said fluid channel ( 2 ) comprises at least two apertures to provide a flow in said channel, where said microelectronic and/or nanoelectronic structure is located within the fluid channel, where said cap is assembled with the substrate at an assembly interface, where said device comprises electrical connections between said microelectronic and/or nanoelectronic structure and the exterior of the fluid channel ( 2 ), where said electrical connections ( 8 ) are formed by vias made through the substrate ( 4 ) directly below the microelectronic and/or nanoelectronic structure, and in electrical contact with said microelectronic and/or nanoelectronic structure.

TECHNICAL FIELD AND PRIOR ART

The present invention relates to a device comprising a fluid channelfitted with at least one microelectronic or nanoelectronic system, andto a method for manufacturing such a device.

Microelectronic or nanoelectronic systems comprise MEMS(microelectromechanical systems) and NEMS (manoelectromechanicalsystems). For the sake of simplification they will be called MEMS andNEMS in the remainder of the description. These systems are now commonlyused in many products. New applications are appearing, particularly dueto the development of NEMS, which provide new benefits due to theirsmaller dimensions. In particular, due to the great mass sensitivity ofthis type of system, they are of great interest for chemical orbiological sensors.

An NEMS or an MEMS comprises a stationary portion and at least onesensitive portion, which may possibly be suspended, relative to thestationary portion.

But for these applications in particular the exposure of the MEMS orNEMS type structure, which provides particular physico-chemicalcharacteristics, to a surrounding environment, generally a gaseous orliquid environment, must be managed. To achieve this the sensitive MEMSor NEMS structure is positioned in a fluid channel in which the mediumflows, allowing the medium to be analysed to be brought into contactwith the sensitive NEMS or MEMS structure.

These sensitive structures are connected to an electronic system forpowering and processing the signals by electrical connections, where thelatter connect the structure to the electronic system, at least aportion of which is located outside the fluid channel.

The fluid channel is produced by adding a cap to a substrate comprisingthe sensitive structure or structures. The cap is sealed in afluid-tight manner on the substrate, and comprises at least twoapertures to allow the fluid to be analysed to flow in the channel. Thecap has a cavity made in a substrate, which is between several μm andseveral hundreds of μm deep, for example.

Document WO2011/154363 describes an analysis device, for example a gaschromatography microcolumn comprising MEMS and/or NEMS in themicrocolumn, forming sensors. The microcolumn is formed of a substrateand a cap. The MEMS and/or NEMS connection is made, for example, by viasmade in the substrate and emerging at the assembly interface between thecap and the substrate. Connection lines connect the vias to thesensitive structures. The presence of these vias at the assemblyinterface makes the assembly complex and, in addition, the electricalconnection of the sensitive structures with the exterior is made complexdue to the production of the vias and of the connection lines.

The cap sealing can use techniques of the polymer sealing, molecularsealing, anode sealing, eutectic sealing, glass sintering, etc. types.The problem is then posed of the production of the electricalconnections between the sensitive structure or structures located insidethe fluid channel and the exterior of the fluid channel since thesealing, whilst allowing these electrical connections, must befluid-tight.

One technique consists, after the cap has been sealed, in opening broadcavities deep within the cap only above areas of metallised contacts toallow direct contact by wirebonding on these contacts, where eachcontact contact is surrounded by a sealing bead, for example one made ofpolymer, to insulate this portion of the cavity. But this technique hasthe disadvantage that it introduces additional patterns for theseelectrical passages inside the fluid channel, which is not desirablesince they can cause disturbances in the flow of the fluid, dead volumesto be generated, etc. Furthermore, this technique is unsuitable in thecase of sensitive structures of the NEMS or MEMS type since thesestructures require small-size semiconductor material or metal contactcontacts to reduce the parasitical capacities and to be able to extracta usable electrical signal with a satisfactory signal-to-noise ratio.Finally, this technique is not suitable for components formed of NEMS orMEMS in networks, since these networks must be interconnected with ahigh density, which implies the use of very small-size contact contacts,and possibly the use of several metal levels.

Another technique to produce these electrical connections whilstguaranteeing tightness consists in producing connections of the Viatype, for example TSVs (Through Silicon Vias) or TGVs (Through GlassVias). Document “3D MEMS high vacuum wafer level packaging—S. Nicolas etal. Electronic Components and Technology Conference (ECTC), 2012 IEEE62nd, Date of Conference: May 29, 2012-Jun. 1, 2012, describes suchmanufacturing. For example, such connections of the TSV type would, forexample, be made deep within the cap and would emerge in the cavity,electrical continuity then being provided by a contact/metal bead insidethe cavity. And such vias would be made in substantial thicknesses ofthe semiconductor material, which can be of the order of several hundredμm, making manufacture of small-sized contacts very difficult. Inaddition, the presence of TSVs traversing the cap and emerging in thefluid cavity can disrupt the operation of the fluid channel, for exampleby disrupting the propagation of the circulating mixture, by disruptingthe chemical properties of the interfaces in contact with the flowingmedium due to the materials of the TSVs, etc. In addition, bearing inmind the dimensions of the channel, in particular the height of thecavity, the electrical connection between the TSV in the cap and thesensitive structure would be difficult to make.

DESCRIPTION OF THE INVENTION

One aim of the present invention is consequently to provide a devicecomprising at least one fluid channel, one or more sensitive structureslocated in the fluid channel, and electrical connections between thesensitive structure or structures located in the fluid channel and theexterior of the fluid channel which does not have the disadvantagesmentioned above.

Another aim is to provide a method for producing such a device withfluid channel.

The aim mentioned above is attained by a structure comprising asubstrate, a cap and an assembly interface between the substrate and thecap, a delimited fluid channel between the substrate, the cap and theassembly interface, at least one sensitive structure located in thefluid channel, and at least one electrical connection between thesensitive structure and an area outside the fluid channel, where theelectrical connection is formed by a via through the substrate in anarea of the fluid channel directly below the microelectronic and/ornanoelectronic structure, outside the sealing interface.

According to the invention, the microelectronic and/or nanoelectronicstructure comprises a stationary structure comprising contact contacts,at least one sensitive structure and means of actuation and/ortransduction of at least one characteristic of the sensitive structure,where the contact contacts are electrically connected to the sensitiveportion and/or to the stationary portion.

The invention simplifies the assembly of the cap and the substrate. Inaddition, by producing the via directly below the microelectronic and/ornanoelectronic structure this via is in direct contact with thecorresponding contact contact. No additional conductive track isrequired between the via and its contact contact. Furthermore, bypositioning the contact in the fluid channel the length of conductivetrack required between the contact and the sensitive portion, orstationary portion, can be limited, and by this means the qualityparticularly of the electrical transduction signal can be optimised.

In addition, in the case of a NEMS/MEMS network each of the NEMS/MEMSstructures present in the fluid channel can be connected directly andindividually, by this means enabling the characteristics of the networkto be controlled and optimised.

In addition, the via or vias do not disturb the flow in the channelsince they do not emerge into the flow of the fluid; they are concealedunderneath the microelectronic and/or nanoelectronic structure. Theinvention therefore enables the production of vias through the capand/or the opening of broad cavities deep within the cap to allowcontact to be avoided.

In other words, the vias are produced through the substrate directlybeneath the microelectronic and/or nanoelectronic structure.

Very advantageously, an intermediate layer can be comprised between thecap and the substrate to facilitate assembly. The intermediate layer canhave a surface state allowing sealing with the faces of the base of thecap, for example a dry film sealing, a molecular or eutectic sealing, ora thermocompression sealing. The face fit for sealing can have a certainroughness or a certain relief which nevertheless allows sealing.

In an equally advantageous manner the intermediate layer can becomprised in the fluid channel, the intermediate layer can be such thatit encapsulates the materials of the NEMS or MEMS structure, except forthe sensitive portion which, due to their presence in the fluid channel,could interact with the medium flowing in the channel, i.e. it isolatesthe materials of the NEMS or MEMS structure other than the sensitiveportion from the interior of the fluid channel. This is the case, forexample, with the metals or dielectrics which are used in the fluidchannel if the mechanical structure comprises a dense network of NEMS.In this case the intermediate layer is advantageously only open in theNEMS or MEMS structures intended to interact with the surroundingmedium.

The sensitive structure can advantageously be functionalised.

In a preferred manner the assembly is produced by means of a dry film;such a method of assembly is particularly suitable if the sensitivestructure is functionalised.

Very advantageously, the via(s) is/are produced after the cap isassembled on the substrate, enabling the substrate to be made thinner,and dense vias to be produced, with the cap acting as a handle.

Furthermore, the structure according to the invention and its productionmethod enable collective production of dies having a fluid channel,where the dies are separated by sawing between the channels and bypre-cuts crossways to the channels.

One subject-matter of the present invention is then a device comprisinga substrate comprising at least one microelectronic and/ornanoelectronic structure comprising at least one sensitive portion andone fluid channel defined between said substrate and a cap, where saidfluid channel comprises at least two apertures to provide a flow in saidchannel, where said microelectronic and/or nanoelectronic structure islocated within the fluid channel, where said cap is assembled with thesubstrate at an assembly interface, where said device comprises at leastone electrical connection between said microelectronic and/ornanoelectronic structure and the exterior of the fluid channel, wherethe electrical connection is formed by a via made at least partlythrough the substrate directly below the microelectronic and/ornanoelectronic structure, and in electrical contact with themicroelectronic and/or nanoelectronic structure.

The via can be in electrical contact with the microelectronic and/ornanoelectronic structure through a contact contact located in the fluidchannel.

The device can very advantageously comprise an intermediate layerlocated at least partly in the fluid channel, where said intermediatelayer covers, in the fluid channel, at least partly the microelectronicand/or nanoelectronic structure, except for its sensitive portion or anintermediate layer located only at the assembly interface locatedbetween the cap and the substrate.

The intermediate layer can comprise an electrical insulating material,such as a silicon oxide, or a silicon nitride.

According to an additional characteristic the device can advantageouslycomprise a functionalisation layer at least partly covering a part ofthe sensitive portion of the microelectronic and/or nanoelectronicstructure.

The device can comprise several microelectronic and/or nanoelectronicstructures interconnected in said fluid channel. The microelectronicand/or nanoelectronic structures can be interconnected byinterconnection lines located in the fluid channel.

The intermediate layer advantageously electrically insulates theinterconnection lines.

In one example embodiment the device comprises a dry sealing filminterposed between the substrate and the cap. The dry sealing film cancomprise several beads.

In another example embodiment the device comprises at least one layer ofmaterial interposed between the substrate and the cap making a eutecticor metallic sealing, or thermocompression sealing, or screen printsealing, or in which the sealing is molecular sealing or glass frit.

The intermediate layer can advantageously comprise at least one firstplanarising layer and one second layer deposited on the first layer,where said second layer is made of a material such that is not verysensitive, or is insensitive, to a step of release of themicroelectronic and/or nanoelectronic structure. The first layer issufficiently thick to efface the variations of topology, and it isadvantageously insulating when the intermediate layer is on the contactcontacts of the microelectronic and/or nanoelectronic structure.

The channel can advantageously form a gas chromatography microcolumn.

Another subject-matter of the present invention is a method formanufacturing at least one device according to the invention, comprisingthe following steps:

a) production of at least one microelectronic and/or nanoelectronicstructure on a substrate,

b) production of a cap comprising a fluid channel, in a cap substrate

c) sealing of the cap and of the substrate such that the microelectronicand/or nanoelectronic structure is located in the fluid channel,

d) production of at least one via in the substrate directly below themicroelectronic and/or nanoelectronic structure.

Step d) can take place after step c) or before step c).

Production of the via can comprise at least

-   -   The step of production of a hole in at least a portion of the        substrate    -   The step of filling all or part of said hole with an        electrically conductive material.

The method can comprise, prior to the production of the at least onevia, and after step d), a step of thinning of the substrate.

The method can comprise, prior to the step of filling of said hole withan electrically conductive material, a step of deposition on the innersurface of the hole of an electrically insulating material.

For example the hole is produced by deep etching followed by fineetching.

If the sensitive portion of the microelectronic and/or nanoelectronicstructure is suspended, where this portion is, for example, releasedbefore step c).

The method can also comprise a step of formation of an intermediatelayer on the substrate after step a) in an area such that it comprisesat least one portion located in the fluid channel after step d) or astep of formation of an intermediate layer on the substrate after stepa) in an area such that it is located only at the assembly interfaceafter step d).

The method can comprise, in step a), production in the microelectronicand/or nanoelectronic structure of at least one electrical contactcontact intended to provide an electrical contact with the via. Themethod can then also comprise, to form said contact contact, anadditional metal deposition on the contact.

The method can also comprise a step of production of an electricaldistribution layer on the face of the device in which said via emerges.

The method preferably comprises a step of production of afunctionalisation layer inside the fluid channel on the microelectronicand/or nanoelectronic structure and/or on the walls of the cap and/or onthe intermediate layer, where said step is accomplished before sealing.

As a variant, the functionalisation layer can possibly be produced aftersealing.

In one example embodiment the sealing step uses a dry film, and theproduction method then comprises the following sub-steps:

-   -   lamination of the dry film on the base faces of the walls of the        cap,    -   structuring of the dry film,    -   bringing the cap and the substrate with the microelectronic        and/or nanoelectronic structure(s) closer,    -   application of a pressure so as to press the dry film.

In another example embodiment the sealing is an eutectic or metalsealing, thermocompression sealing, or a molecular sealing or screenprint sealing.

Several devices can be produced simultaneously; the substrate thencomprises several microelectronic and/or nanoelectronic structures andthe cap substrate comprises several caps, where the caps are sealedsimultaneously on the substrate comprising the microelectronic and/ornanoelectronic structures, such that a fluid channel of a device can orcannot communicate with the fluid channel of other devices.

The method can comprise the following steps:

-   -   a step of production of pre-cuts in a direction perpendicular to        the fluid channels in the cap substrate and in the substrate,    -   a step of separation of the devices, advantageously by cleavage.    -   a step of pre-cutting or of cutting in a direction parallel to        the fluid channels between the channels,    -   a step of separation of the devices, advantageously by cleavage        of the pre-cuts.

BRIEF DESCRIPTION OF THE ILLUSTRATIONS

The present invention will be better understood using the descriptionwhich follows and the appended illustrations, in which:

FIG. 1 is a top view of a device with fluid channel comprising MEMS/NEMSstructures according to one example embodiment of the invention,

FIG. 2 is a cross-section view of the device of FIG. 1 along plane A-A′,

FIG. 3 is a cross-section view of a device according to a variant of thedevice of FIG. 1, in which a non-localised functionalisation layer isimplemented,

FIG. 4 is a cross-section view of a device according to a variant of thedevice of FIG. 1, in which a non-localised functionalisation layer isimplemented,

FIG. 5A is a top view of a device with fluid channel comprisingMEMS/NEMS structures according to another example embodiment of theinvention implementing an intermediate layer between the cap and thesubstrate,

FIG. 5B is a cross-section view of the device of FIG. 5A along planeB-B′,

FIG. 6 is a cross-section view of a device according to a variant of thedevice of FIG. 5A, in which a non-localised functionalisation layer isimplemented,

FIG. 7 is a cross-section view of a device according to a variant of thedevice of FIG. 5A, in which a localised functionalisation layer isimplemented,

FIG. 8A is a top view of a device with fluid channel comprisingMEMS/NEMS structures according to another example embodiment of theinvention implementing an intermediate layer between the cap and thesubstrate, extending within the channel, and delimiting a longitudinalarea without an intermediate layer,

FIG. 8B is a top view of a variant of the device of FIG. 8A, where theinterior of the channel, except for the sensitive portion of theMEMS/NEMS structure, is covered by the intermediate layer,

FIG. 8C is a cross-section view of the device of FIG. 8A or that of FIG.8B, along plane CC′,

FIG. 9 is a section view of a device according to a variant of thedevice of FIG. 8C, in which a non-localised functionalisation layer isimplemented,

FIG. 10 is a cross-section view of a device according to a variant ofthe device of FIG. 8C, in which a localised functionalisation layer isimplemented,

FIG. 11A is a top view of a device with fluid channel comprisingMEMS/NEMS structures according to another example embodiment of theinvention implementing an intermediate layer only within the channel,and delimiting a longitudinal area without an intermediate layer,

FIG. 11B is a cross-section view of the device of FIG. 11A along planeDD′,

FIG. 12A is a top view of another example embodiment with a fluidchannel according to the invention, in which several MEMS/NEMSstructures are produced,

FIG. 12B is a cross-section view of the device of FIG. 12A along planeEE′,

FIG. 13A is a top view of a variant of the device with fluid channel ofFIG. 12A, in which an intermediate layer is formed between the substrateand the cap and within the channel,

FIG. 13B is a cross-section view of the device of FIG. 13A along planeFF′,

FIG. 14 is a section view of a variant of the device of FIGS. 12A and12B comprising interconnections between the MEMS/NEMS,

FIG. 15 is a section view of a variant of the device of FIGS. 14A and14B comprising interconnections between the MEMS/NEMS,

FIG. 16 is a section view of another example embodiment of a deviceaccording to the invention, in which the assembly between the cap andthe substrate is produced by means of a dry film,

FIG. 17 is a section view of a variant of the device of FIG. 16comprising an intermediate layer is formed between the substrate and thecap and within the channel,

FIG. 18 is a section view of a variant of the device of FIG. 16comprising several MEMS/NEMS and an intermediate layer is formed betweenthe substrate and the cap and within the channel,

FIGS. 19A to 19H are diagrammatic representations of steps of an exampleof a method for producing the substrate fitted with at least one MEMS orNEMS structure for the production of a device with fluid channelaccording to the invention,

FIGS. 20A to 20D are diagrammatic views of steps of an example of amethod for producing a cap and its assembly with the substrate havingthe MEMS or NEMS structure(s) for the production of a device with fluidchannel according to the invention,

FIGS. 21A to 21F are diagrammatic views of steps of an example of amethod for producing vias in the assembly of FIG. 20D,

FIGS. 22A to 22C are diagrammatic representations of steps of an exampleof a method for producing a device with fluid channel according to theinvention having no intermediate layer,

FIGS. 23A to 23F are diagrammatic representations of steps of an exampleof a method for producing a device with fluid channel according to theinvention having no intermediate layer.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

In the present application the term “NEMS/MEMS portion” is understood tomean a mechanical structure comprising a stationary structure and atleast one sensitive structure, and means of actuation and/ortransduction of at least one characteristic of the sensitive structure.

Electrical connections are provided to connect the sensitive structureto the external environment. This MEMS/NEMS portion may comprise anetwork of NEMS and/or MEMS structures, possibly with severalmetallisation levels to produce the required interconnections. Forpurposes of simplicity, an MEMS or an NEMS will be designated by NEMS.

The “sensitive portion” can be a suspended portion or a portion which isnot suspended. In the remainder of the description these two expressionswill be used interchangeably, bearing in mind that in certainapplications of the electromechanical type this sensitive portion ismobile.

The term “NEMS structure” is understood to mean, in the presentapplication, a structure comprising one or more NEMS.

The same references will be used to designate the elements having thesame functions and approximately the same shape.

In the represented examples the fluid channel is linear along axis X,but a channel having a curved shape, or indeed a spiral or any othershape, does not go beyond the scope of the present invention.

In FIG. 1 a device with fluid channel according to a first embodimentcan be seen represented diagrammatically, as a top view, with the top ofthe cap omitted. In FIG. 2 a cross-section view along plane A-A′ of FIG.1 can be seen. In this view the top of cap 6 is represented.

The device comprises a fluid channel 2 which is linear along axis X inthe represented example. Fluid channel 2 is delimited by a substrate 4and a cap 6 added on to substrate 4 and assembled in an area of anassembly interface 3. For example, the flow in the fluid channel occursfrom one longitudinal end 2.1 to the other 2.2 of fluid channel 2.

In the represented example cap 6 is formed from a substrate in which acavity 5 has been made. Cavity 5 delimits with the substrate bearing theNEMS/MEMS structure and assembly interface 3 fluid channel 2 whichcauses a gas mixture or liquid blend to flow and be distributed. Thechannel is delimited by two side walls 6.1, where an upper base 6.2connects the two side walls 6.1 and a lower base formed by substrate 4.Side walls 6.1 have under-faces which allow the cap to be sealed on tothe substrate.

It will be understood that the input end and/or the output end of thefluid channel could, for example, be produced in the upper base 6.2 ofthe channel or alternatively in substrate 4.

Alternatively, cap 6 could have a more complex shape, for example itcould comprise a long channel of optimised shape, for example a spiral,enabling a chromatography column to be produced implementing thefunction of separation of the compounds of a mixture, where the columncomprises one or more NEMS/MEMS structures.

In the represented example cap 6 is assembled on to substrate 4 bysealing.

The substrate comprises a NEMS/MEMS structure 7 located inside fluidchannel 2. In the represented example the suspended structure of theNEMS is formed by a beam 10 which is embedded at one of its longitudinalends; for example two gauges 12, for example two piezoresistive gauges,are used to detect the movement of beam 10. The ends of connection lines8 connected to the NEMS/MEMS structure can be seen

The device also comprises electrical connections 8 extending between theNEMS located in fluid channel 2 and the exterior of the fluid channel.Electrical connections 8 are formed by vias running through substrate 4,also called TSVs (Through Silicon Vias). For purposes of simplicity thevias running through substrate 4 will subsequently be designated “via”.The vias run through substrate 4 vertically below the NEMS structurelocated in the fluid channel and outside the assembly area, morespecifically vertically below the stationary portion of the NEMS. In therepresentation of FIG. 2 the vias are produced under the NEMS.

The vias are preferably produced using a via-last approach, i.e. afterproduction of the NEMS structure(s). The vias then have a diameter ofseveral μm; they are well suited to the mechanical structures and theyhave relatively high densities since the interval between these vias isof the order of some ten μm. The vias can be made of different materialssuch as, for example, Cu, W, etc.

As a variant, vias of different natures and geometries can be envisaged.For example, the vias can be wide etched holes covered with a conductivematerial providing the electrical continuity between the two faces ofthe substrate. Alternatively, and preferentially, the vias can be formedby relatively narrow holes which are completely filled with a more orless conductive material, for example polysilicon. A narrow hole has,for example, a diameter of approximately several μm and a wide hole has,for example, a diameter of approximately several tens of μm to severaltens of μm. As another variant it can be envisaged, for example, toretain the semiconductor material in which the via is formed, and tofill the annular peripheral area which surrounds the semiconductormaterial with an electrically insulating material to insulate thecentral portion relative to the remainder of the substrate.

For example, the via(s) can come into contact with the lower face oflayer 16 in which the NEMS is/are formed. As a variant, the via(s) cancome into contact with the upper face of layer 16, preferentiallythrough a metal contact formed on the surface of layer 16.

As another variant, the via(s) can come into contact on a metalinterconnection layer produced in a plane parallel to the plane of theNEMS, on the side of the fluid channel, for example on one of the levelsof interconnection of the NEMS networks which will be described below,or on the side of the substrate in which these connection patterns areproduced. It could also be envisaged for the vias to come into contacton a metal interconnection layer produced in a plane parallel to theplane of the NEMS, but on the side opposite the fluid channel, toconnect to external elements located, for example, to the rear of theMEMS

Substrate 4 comprises a stack of a sacrificial layer 14 used to producethe NEMS, a layer 16, for example made of a semiconductor material, inwhich the stationary portion and the suspended portion of the NEMS areproduced.

The vias do not emerge in assembly interface 3, and the assemblyinterface can then have no metal layer. It is then possible to produceassemblies with sealing techniques which are very efficient in terms ofrobustness, reliability and hermeticity.

Firstly, the fact that no via emerges in the sealing or connection linesinterface between the cap and the substrate enables a flat surface to beprovided. Thus, techniques such as molecular sealing, eutectic sealing(AuSn, AuSi, etc.) or metal thermocompression sealing (Au—Au, Al—Ge) canbe envisaged. Metal thermocompression sealings are particularlyadvantageous since they enable the sealing temperature to be reducedbelow 400° C. or even 200° C., which is particularly advantageous when afunctionalisation layer is implemented. Similarly, a molecular sealing,which can be undertaken at low temperature, is advantageous for the samereasons of preservation of a possible functionalisation layer.

If the deposition of a layer is required for the sealing, where thislayer can possibly be structured on a single one of the two portions,which is the case for a eutectic sealing, this deposition and thispossible structuring are preferably undertaken on the cap. For example,in the case of an Au—Si eutectic sealing, a layer of Au is preferablydeposited on the cap.

If deposition of a layer on each of the two portions is required, forexample for a thermocompression sealing, deposition on the NEMS/MEMSstructure is undertaken before the structure is released. The materialof this layer is then chosen such that it is compatible with the methodof release of the NEMS/MEMS structure, so that it is not etched in thistechnological step which occurs just before sealing. A layer of Au willthen be used on the cap and on the intermediate layer for an Au—Ausealing, if the NEMS is to be released with vapour phase hydrofluoricacid.

In the case of a molecular sealing or anodic sealing, for example if thecap is made of glass, the sealing interface is formed by the face of thecap and the face of the substrate which is to be sealed. No addition ofmaterial is required. The faces intended to come into contact areprepared in a known manner by those skilled in the art, for example byCMP (chemical-mechanical polishing) of layer 16 and of the lower face ofcap 6.

A molecular sealing in the presence of a functionalisation layer at theinterface, where the functionalisation layer is also deposited afterrelease, is also conceivable.

The vias are advantageously produced after the cap is sealed on to thesubstrate. In this case high-temperature sealings are conceivable,particularly since there are no active structures of the CMOS type onthe substrate.

In addition, the use of vias in the fluid channel enables devices to beproduced with a larger number and/or a higher density of electricaloutputs of the NEMS structures contained in the fluid channel towardsthe exterior of this channel. This therefore results in the possibilityof having a higher density of NEMS structures (whether or not innetworks) inside the fluid channel, which is particularly advantageousin the case of a gas chromatography microcolumn in which NEMS/MEMSstructures are distributed throughout the length of the microcolumn.

As a comparison, relative to the lateral connection lines implementingelectrical contact contacts of the order of 100 μm×100 μm, this densitycan be increased by making vias of small diameters, for example severalμm or several 10 μm of diameter.

In addition, as was mentioned above, since the vias are produced in thesubstrate, they are produced independently of the thickness of the “cap”layer. It is then possible to produce dense vias and a deep cavity. Thisadvantage is remarkable in particular in the case of an instrumentedmicrocolumn which requires dense vias, requiring that the NEMS substrateis thinned to some 10 μm, and a dimension of the microcolumn cavities ofat least 100 μm. Indeed, the typical dimensions of the channel sectionare 80×80 μm, or greater, for the requirements of the application toseparate the analytes constituting the gas mixture flowing in thechannel. The vias are advantageously produced after assembly with thecap, which then allows a sufficient thinning of the substrate, forexample of several tens of μm, to produce sufficiently dense vias, withthe cap providing the mechanical rigidity.

The invention makes it possible to manufacture the device with complexNEMS networks within the fluid channel, and to have very satisfactorycontrol of these networks, through individual addressing of each NEMSstructure through the TSVs.

Furthermore, the materials at the sealing interface such as silicon,metals, oxides, etc., are generally more neutral compared to the species(for example gas), flowing in the fluid channel, compared to a layer ofadhesive, which may degas and can have a disruptive chemical affinityrelative to the species in circulation. This advantage is particularlyuseful in the example of a fluid channel intended for the production ofa gas chromatography column.

In FIG. 3 the device comprises a functionalisation layer 18 coveringlayer 16, and the entire NEMS/MEMS structure. This functionalisationlayer 18 is said to be non-localised.

The term “functionalisation layer” is understood to mean a layer presentat the surface of the mechanical structure, to give it particularproperties. For example, in the case of a gas sensor, thefunctionalisation layer enables the adsorption of gas species, possiblyselectively, to be increased or, in the case of a biological sensor, thefunctionalisation layer allows the grafting of biological species.Functionalisation layer 18 is, for example, formed of one or moreorganic or inorganic materials, polymers, oxides, carbon compounds,semiconductors or other porous materials.

The invention allows, very advantageously, the step of deposition of thefunctionalisation layer to be implemented on a previously releasedmechanical structure, which enables the mechanical structure to beencapsulated almost totally with the functionalisation layer when thedeposition of this layer is sufficiently conformal. Thefunctionalisation layer then has a surface which interacts to a greaterdegree with the surrounding medium, which increases still further theusefulness of a functionalisation layer. The invention allows theimplementation of functionalisation layers on NEMS released bycollective techniques without liquid contact, for example by CVD, LPCVD,PECVD or ALD, epitaxy, porosification, etc. and this to be followed byclosing the component by adding a cap with a cavity so as to form thefluid channel. By this means the risks of adhesion by deposition of thefunctionalisation layer by deposition in the liquid phase are prevented.

In FIG. 4 functionalisation layer 118 is present only on the sensitiveportion of the NEMS, and the functionalisation layer is said to belocalised.

The invention allows, very advantageously, the step of deposition of thefunctionalisation layer to be implemented on a previously releasedmechanical structure, which enables the mechanical structure to beencapsulated almost totally with the functionalisation layer when thedeposition of this layer is sufficiently conformal. Thefunctionalisation layer covers the upper face, the lower face and theside faces of the suspended element. The functionalisation layer thenhas a surface which interacts to a greater degree with the surroundingmedium, which increases still further the usefulness of afunctionalisation layer. The invention allows the implementation offunctionalisation layers on NEMS released by collective techniqueswithout contact, for example by CVD, LPCVD, PECVD or ALD, epitaxy,porosification, etc. and this to be followed by closing the component byadding a cap with a cavity so as to form the fluid channel. By thismeans the risks of adhesion by deposition of the functionalisation layerby deposition in the liquid phase are prevented.

In FIGS. 5A and 5B a device according to a particularly advantageousembodiment of the invention can be seen implementing an additional layer20 called an “intermediate layer”.

According to a first example represented in FIGS. 5A and 5B,intermediate layer 20 is positioned at the assembly interface only. Itis interposed between layer 16 made of a semiconductor material and cap6. The presence of intermediate layer 20 at the assembly interfacefacilitates assembly. Indeed, the intermediate layer can have a surfacecondition allowing sealing with the faces of the base of the cap, forexample a dry film sealing, a molecular, eutectic or thermocompressionsealing. The face fit for sealing can have a certain roughness or acertain relief which nevertheless allows sealing.

Intermediate layer 20 is present at least at the sealing interfacebetween NEMS/MEMS structure 7 and the cap and is absent from thesensitive areas of the NEMS/MEMS structure, in order to leave theportion or portions of the suspended NEMS/MEMS structure in contact withthe medium present in the fluid channel.

The material of intermediate layer 20 is chosen such that it is possibleto obtain a face 20.2 which is sufficiently flat for sealing the cap.Depending on the type of sealing, the surface condition of face 20.2obtained directly after the deposition of the intermediate layer can besufficient, or a step of planarisation is accomplished, for example astep of chemical-mechanical polishing after the formation of theintermediate layer.

The material of the intermediate layer is chosen such that it can beetched, for example by anisotropic etching.

The material of intermediate layer 20 is preferably chosen such that ithas a satisfactory etching selectivity compared to the method of releaseof the mechanical structures, and does not generate any residue in thisstep.

The material of the intermediate layer is also chosen such that it iscompatible with the materials used for the final assembly of the devicebetween the substrate bearing the NEMS/MEMS structure and the cap.

If a functionalisation layer is implemented, the material of theintermediate layer is chosen such that it is compatible with that of thefunctionalisation layer, in particular so as to provide satisfactoryadherence of the latter.

For example, the material of the intermediate layer is a dielectricmaterial, for example a silicon oxide, such as for example SiO₂ or anoxide formed from silane or an oxide formed from tetraethylorthosilicate (TEOS), a silicon oxide of the LTO (Low Temperature Oxide)type formed by LPCVD (Low Pressure Chemical Vapour Deposition), which iseither undoped or alternatively doped with phosphorus (PSG:Phospho-Silicate-Glass) or again doped with boron and phosphorus (BPSG:Boro-Phospho-Silicate Glass), an oxide deposited by PECVD (PlasmaEnhanced Chemical Vapour Deposition).

The thickness of the intermediate layer is determined taking account ofthe consumption of the material during the release etching. In this casethe thickness of the intermediate layer is, for example, of the order ofseveral μm.

As a variant the intermediate layer can comprise two layers. A layer ofdielectric material forming the planarising layer is deposited. Theplanarising layer is, for example, an oxide formed from silane SiH₄, oralternatively an oxide formed from tetraethyl orthosilicate (TEOS). Aprotective layer, made for example of amorphous Si, silicon nitride,metal (AlSi, AlCu, etc.) or hafnium oxide (HfO2), is then deposited onthe planarising layer, and the latter increases the resistance toetching using hydrofluoric acid vapour.

In FIG. 6A a variant embodiment can be seen in which a non-localisedfunctionalisation layer 18 is produced; it is then located on face 20.2of the intermediate layer.

In FIG. 7 a variant embodiment can be seen in which a non-localisedfunctionalisation layer 118 is produced; it is located only on thesensitive portion of the NEMS.

In FIGS. 8A, 8B and 8C, another example embodiment of a deviceimplementing an intermediate layer can be seen. In this exampleintermediate layer 120 is located at the sealing interface and insidethe fluid channel.

In FIG. 8A the intermediate layer delimits a channel 21 within thechannel with a width such that it leaves the sensitive portions of theNEMS structure free.

In FIG. 8B the intermediate layer leaves free only the sensitiveportions of the NEMS structure, and the intermediate layer is presentupstream and downstream of the NEMS structure.

In this example embodiment, in addition to its presence at the sealinginterface, the intermediate layer encapsulates the materials used in theNEMS, leaving accessible for the fluid circulating in the fluid channelonly the sensitive portion of the NEMS or of a network of NEMS.

This encapsulation has the advantage that it isolates the materials usedin the NEMS portion which, through their presence in fluid channel 2,could interact with the medium circulating in the channel. This is thecase, for example, with the metals or dielectrics which are generallyused in the fluid channel if the mechanical structure is formed of adense network of NEMS.

A device with fluid channel in which the intermediate layer does notentirely cover the portion of the NEMS/MEMS structure not intended tocome into contact with the surrounding medium does not go beyond thescope of the present invention.

By this means the interactions between the materials used in the NEMSand the medium present in the fluid channel are prevented.

In addition, the intermediate layer forms a quasi-flat surface in thearea surrounding the sensitive portions of the NEMS, forming a fourthface of the fluid channel.

As can be seen in particular in FIG. 8C, intermediate layer 120 ispresent above layer 16 in which the NEMS is produced, which is made forexample of a semiconductor material, in the area of the vias which are,for example, made of metal. The presence of the intermediate layermechanically strengthens the structure, in particular with regard to themechanical stresses which can be caused in the vias, for example due todifferences of thermal expansion coefficient between the material of thevias and the surrounding material in which these vias are formed. Thereliability of the device is then improved.

In FIG. 9 a variant embodiment can be seen in which a non-localisedfunctionalisation layer 18 is produced; it is then located on face 120.2of the intermediate layer.

In FIG. 10 a variant embodiment can be seen in which a non-localisedfunctionalisation layer 118 is produced; it is located only on thesensitive portion of the NEMS.

In FIGS. 11A and 11B another example embodiment of a device implementingan additional layer, called the “encapsulation layer”, 220 can be seen,which is present only inside the fluid channel, and covers the materialsused in the NEMS.

Encapsulation layer 220 has the same advantages as layer 120, except forthose relating to the sealing.

In a manner similar to the variants of FIGS. 9 and 10, the device ofFIGS. 11A and 11B can comprise a functionalisation layer eitherlocalised on the sensitive portions of the NEMS structure, or notlocalised; it would then be located at the assembly interface, onencapsulation layer 220 and the sensitive portions of the NEMSstructure.

In FIGS. 11A and 11B an example embodiment of a device implementingmultiple NEMS in the fluid channel can be seen. The NEMS may or may notbe interconnected. An example of a device with interconnected NEMS willbe described below.

In the represented example three pairs of NEMS are aligned along axis X.

In FIGS. 12A and 12B an example embodiment of a device with several NEMSstructures 7 can be seen, where each of these structures can beconnected to a via. It should be noted that in FIGS. 12A and 12B thereare no metal interconnections on the side of the fluid channel, nor anyrepresented intermediate layer. However, such an intermediate layer canbe implemented in the different configurations described above.

For example, in FIGS. 13A and 13B an intermediate layer 120 is formedbetween the cap and the substrate and in the channel, leaving free onlythe sensitive portions of the NEMS structures.

In FIG. 14 a device comprising a network of interconnected NEMS can beseen. In this example the interconnections between NEMS are made byconductive connections, preferably metal connections, 24, formed on theNEMS in the fluid channel.

Interconnection lines 24 are then made on several levels of metal, twosuch in the represented example, in order to interconnect the NEMSforming the network of NEMS, which is located inside the fluid channel.Interconnections with one or more than two metal levels do not go beyondthe scope of the present invention.

This configuration enables the flatness of the surfaces surrounding theNEMS to be preserved, and in particular the assembly interface, by thismeans facilitating assembly of the cap and of the substrate. The via(s)can come into contact on one of the connection lines, as describedabove.

As a variant, the NEMS can be interconnected electrically, eitherdirectly through connection patterns 8 and/or through interconnectionpatterns in addition to the device of the invention, or by meanscomprised in the device, for example by an electrical routing layerformed on rear face I, or by means external to the device, for exampleby an electronic card or an integrated circuit connected to the deviceby flip-chip or copper pillar techniques, or other techniques well knownto those skilled in the art in the 3D integration field.

As another variant, the NEMS can be interconnected throughinterconnection lines made in the material of layer 16 and/or throughone or more metal layers produced in the planes parallel to layer 16. Inthe latter case the metal interconnections can be electrically insulatedfrom one another by air, or indeed one or more dielectric materials.

In FIG. 15 a variant of the device of FIG. 14 can be seen in which anintermediate layer 120 is implemented. Very advantageously theelectrical connections are encapsulated by intermediate layer 120 in anelectrically insulating material, for example made of silicon oxideleaving only the sensitive portions accessible. This encapsulationenables the materials of the interconnections to be insulated from thefluid flowing in the channel, and by this means enables undesiredreactions with it to be prevented. This intermediate layer also forms afourth face of the fluid channel.

The different metallisation levels are partially encapsulated inelectrically insulating layer 120 made, for example, of silicon oxide.

This encapsulation by the intermediate layer is particularlyadvantageous to implement in the case of NEMS which are interconnectedby conductive tracks made of semiconductor material or of metal,possibly with several levels of interconnections, where the electricalinsulation between the levels is provided by layers of dielectrics, andthe whole assembly is localised in the fluid channel.

In FIGS. 16 to 18 devices can be seen represented in which the assemblyis accomplished by means of a Dry Film Resist or DFR 22.

For example, a thin resin film is applied by lamination on to the lowerface of cap 6 intended to come into contact with layer 16 (FIG. 16) orintermediate layer 20 (FIGS. 17 and 18) and is structured byphotolithography and development. The cap and resin film assembly istransferred and sealed on the substrate.

In the example represented in FIGS. 16 to 18 thin film 22 takes the formof two parallel beads, having roughly the same sealing area. These beadsare obtained after insolation and development of the dry film.

The dry film is, for example, a resin with epoxy, phenol, acrylic orsilicone bases, for example.

The dry film is, for example, between several μm and several tens of μmthick, or several hundreds of μm thick with a multi-layer of dry film,and advantageously only several μm thick.

Sealing by means of a dry film has the following advantages:

-   -   this type of sealing can take place at a relatively low        temperature, generally below 250° C., or at ambient temperature,        which is compatible with the existence of metal tracks. Indeed,        in the case of aluminium tracks the maximum temperature is 400°        C.    -   this type of sealing is compatible with a large number of        materials,    -   the dry film can be produced on the cap despite the strong        topology due to the previously formed fluid channel, which        enables no operations of the photolithography type to be        undertaken on the NEMS/MEMS structure, since the latter already        contains released mechanical structures,    -   this type of sealing by dry film has the advantage that it is        less demanding in terms of the required surface condition        (flatness, roughness, presence of particles) at the sealing        interface than sealings of the molecular or eutectic type, or        even thermocompression sealings. Thus the use of a dry film can        allow sealing without undertaking any prior chemical-mechanical        polishing of the face of the substrate on which the sealing is        accomplished, for example face 20.2 of the intermediate layer        (FIGS. 17 and 18), and its surface condition directly after        deposition can be sufficient.

This characteristic advantageously enables this sealing to beaccomplished in the presence of a functionalisation layer at theassembly interface. In addition, the temperature of such sealing iscompatible with the presence of a functionalisation layer which isdeposited or itself formed at low temperature, for example made ofpolymer, etc.

-   -   This type of film also provides the possibility of working with        large thicknesses, for example of the order of several hundreds        of μm, but also thicknesses of several 10 μm; or several μm,        since a small thickness enables the thickness of the material of        the dry film able to interact with the surrounding medium to be        limited.    -   This type of film also has satisfactory thermal stability.    -   In addition, since this type of sealing is compatible with a        large number of materials, great freedom is available in the        choice of functionalisation layer or layers which can be        implemented. It is then possible to envisage implementing        functionalisation layers of different natures and/or thicknesses        on the NEMS and cap portions. This is particularly advantageous        if the cap forms a gas chromatography column. In this case the        cap will be able to receive a functionalisation which is able to        fulfil the function of separation of the analytes of the mixture        or blend to be analysed, while the NEMS will be able to receive        another functionalisation able to optimise its detection        efficiency.

If a functionalisation layer is implemented the sealing isadvantageously accomplished by the dry film technique.

We shall now describe examples of methods of producing devices withfluid channel according to the present invention.

The method which will be described allows the production of several NEMSsimultaneously in a fluid channel aligned along the longitudinal axis,where a single one is visible. It will be understood that the methodallows the production of several devices simultaneously with one or moreNEMS, where the devices are then separated at the end of themanufacturing method.

In a first phase the substrate comprises the NEMS/MEMS structure isproduced from an SOI (Silicon On Insulator) substrate, for example.Alternatively, any substrate comprising a layer in which the NEMS/MEMSis produced can be used, where this layer is formed on a sacrificiallayer allowing release of the NEMS/MEMS structure through etching of it.The material of the layer in which the NEMS/MEMS structure is producedcan be a monocrystalline or polycrystalline semiconductor material, forexample Si, Ge, SiGe, SiC, GAAs, InAs, InP, etc. The sacrificial layercan be present over the whole substrate, or alternatively be localisedonly at certain places where the NEMS will be produced.

It can be envisaged that the NEMS/MEMS structure comprises an opticalfunction so as to comprise MOEMS (Micro-Opto-Electro-Mechanical Systems)and/or comprise an integrated electronic portion, CMOS, etc.

The first example of a method which will be described enables a deviceaccording to the invention to be produced comprising an intermediatelayer and a localised functionalisation layer with a level ofinterconnections in the area of the NEMS as represented for example inFIG. 7.

The SOI substrate comprises a layer of insulating material 28, forexample made of silicon oxide, and a silicon layer 30 in which the NEMSstructure will be formed.

In a first step the silicon layer 30 is doped. To accomplish this aprotective oxide layer is formed on doped layer 30, for example athermal oxide, followed by a step of implantation, followed by annealingand deoxidation by removal of the oxide layer.

The doping can be accomplished in a full-plate manner or using masking,for example using a resin if it is desired to localise areas withdifferent types of doping. For example it is possible to envisage amedium to moderate (several 10¹⁸ to several 10¹⁹ at/cm³) P-type doping(boron, for example) or N-type doping (phosphorus, for example) in theNEMS area, depending, for example, on whether it is desired to optimisethe piezoresistive gauge factor and/or the noises, and a strong doping(several 10²⁰ at/cm³) in the area of the contact contacts intended toreceive the metal of the vias on their lower face, so as to provide asatisfactory ohmic contact.

The element obtained in this manner is represented in FIG. 19A.

In a subsequent step the NEMS structures and the electrical contactcontacts are defined.

To do so a photolithograph and then an anisotropic etching of siliconlayer 30 are accomplished in a known manner.

A step of stripping then takes place on the silicon and on oxide layer28 to remove the layer of photosensitive resin.

The element obtained in this manner is represented in FIG. 19B. In FIG.19B, which is a section view, a single NEMS can be seen, but thestructure preferably comprises multiple NEMS in direction X. Thestructure could also comprise several NEMS in a direction perpendicularto direction X.

In the next steps the metal interconnection lines are made. To do so adeposition of a dielectric layer 32 on structured layer 30 then takesplace; this is, for example, an oxide formed from silane SiH₄ thethickness of which is greater than the topology of structured siliconlayer 30.

A step of chemical-mechanical polishing or CMP then takes place to makethe surface of layer 32 flat. Prior to this a photolithograph of the“counter mask” type and a partial etching of layer 32 of the height ofthe topology to be made up are preferably undertaken, which facilitatesthe step of polishing, and enables its duration to be reduced.

In a subsequent step layer 32 is opened by photolithography and etchingto reach silicon layer 30, and to prepare for the production of theelectrical contact contacts and/or the interconnection lines betweenNEMS.

The element obtained in this manner is represented in FIG. 19C.

In a subsequent step, a metal layer 34 is deposited, made for example ofAlSi, since the latter has the advantage that it provides satisfactoryresistance to the etching by hydrofluoric acid vapour, which takes placeto release the mechanical structures. The thicknesses of formed layersare chosen so as to facilitate subsequent planarisation.

In a subsequent step chemical-mechanical polishing takes place.

The element obtained in this manner is represented in FIG. 19D.

In the represented example layer 32 is preserved. As a variant it can beremoved, and advantageously etched selectively relative to the metal ofthe interconnection lines, in order to preserve the interconnectionand/or metallisation lines of the contact contacts. It can be fullyremoved or removed only partially, for example in the areas intended forthe assembly. The steps of production of the contact contacts and/or ofthe interconnection lines can be repeated several times in order toproduce several levels of metal interconnections. These steps can alsoenable electrical interconnection lines to be produced between differentNEMS on one or more levels. The interconnection lines are then insulatedfrom one another by the material of layers 32.

The subsequent steps describe the production of intermediate layer 20.

In the represented example intermediate layer 20 has two layers. A layerof dielectric material 35 is deposited, for example a silicon oxideformed from silane SiH₄, or alternatively a silicon oxide formed fromtetraethyl orthosilicate (TEOS). A protective layer 36, made for exampleof amorphous Si, silicon nitride, metal (AlSi, AlCu, etc.) or hafniumoxide (HfO2), is then deposited on the planarising layer, and the latterincreases the resistance to etching using hydrofluoric acid vapour usedto release the NEMS.

In the case of an intermediate layer made of a single material itsthickness is determined such that it is able to protect, in particular,the connection lines in the final step of release of the mechanicalstructures, i.e. its thickness is chosen such that it is sufficient totake account of the reduction due to the release etching, in order thatit still covers the connection lines. As mentioned above, the thicknessof the intermediate layer in this case can be, for example, of the orderof several μm.

In this example intermediate layer 20 is formed on metal interconnectionlines and/or electrical contact contacts, but it could be implementeddirectly on the NEMS layer (with or without metal interconnection linesor electrical contact contacts), etc. It should be noted that layer 32could have been removed after formation of the interconnection lines;intermediate layer 20 would then have been formed directly on theselines.

The element obtained in this manner is represented in FIG. 19E.

A step of polishing, for example by CMP, of layer 32 prior to thedeposition of layer 20 can take place.

In a subsequent step the intermediate layer is etched so as to reach theNEMS/MEMS structure to be released. Layer of amorphous Si 36 and layer35 are etched, and layer 32 can also be partially or totally etched. Forexample, it is possible to use an SF₆ plasma etching for the layer ofamorphous Si and a CHF₃ plasma etching for the etching of the siliconoxide forming the intermediate layer.

Intermediate layer 20 can be etched in different ways to produce thedifferent devices described above. It is thus possible to etch it onlyabove the sensitive portions by protecting the remainder of the surface,in order that the intermediate layer is at the assembly interface and inthe fluid channel, or then only at the assembly interface or,alternatively, only in the fluid channel, in which case it has solely anencapsulation function.

Etching of intermediate layer 20 is chosen so as to preserve both themetal interconnections and the NEMS/MEMS structure made of asemiconductor material. In this manner the shape of the apertures isdetermined for example by photolithography so as to take account of thelength of release of the mechanical structures which occurs at the endof the “NEMS” method, since this step can cause an undesired lateraletching of the planarising layer of intermediate layer 20 which, if itwere not controlled, could lead to the release of undesired areas suchas metal interconnections, areas under the sealing interface with thecap. In addition, etching of the aperture in the intermediate layer ispreferably stopped in the metal layer above the semiconductor, beforereaching the semiconductor, in order that the semiconductor layerconstituting the mechanical structure is not damaged.

The element obtained in this manner is represented in FIG. 19F.

In a subsequent step the NEMS/MEMS structure, in particular mobileportion(s) 10, is/are released. Release takes place, for example, byisotropic etching using hydrofluoric acid vapour of the dielectricmaterials surrounding the NEMS structure; these are layers 28 and 32.Layer 28 can be totally or partially etched. Due to the presence ofprotective layer 36 layer 35 is protected and its thickness is notreduced.

The element obtained in this manner is represented in FIG. 19G.

In FIG. 19H the element of FIG. 19G is represented comprising afunctionalisation layer 118 which is localised on suspended portion 10of the NEMS. As a variant, this layer could be non-localised. As avariant it is also possible not to have any functionalisation layers.

This functionalisation layer can be produced in different ways by liquidor gaseous phase depositions. Techniques of gas phase deposition, forexample by CVD (Chemical Vapour Deposition), by LPCVD, by PECVD, or byALD (Atomic Layer Deposition), etc. are preferentially used. Techniquesof epitaxy and/or of porosification of materials and/or of theevaporation type can also be implemented. These techniques arepreferable to the liquid techniques, of the spraying or spotting type,since they enable the use of liquid phases in the presence of releasedNEMS structures to be avoided. However, these latter techniques can alsobe used, for example if the NEMS/MEMS structures are sufficiently rigid.

The deposited materials forming the functionalisation layer(s) can, forexample, be materials of the polymer type, dielectrics, semiconductormaterials or other porous materials, metals, etc.

In the case of a localised deposition, mechanical masking (stencil)techniques can be used, or lift-off techniques known in methods forproducing microsystems, or again spotting techniques, consisting indepositing drops of liquid solution locally, etc.

In FIG. 19H the functionalisation layer is represented only at thesurface of the NEMS. The functionalisation layer preferentiallysurrounds the NEMS, and the thickness of the functionalisation layer isnot necessarily uniform all the way round the mechanical structure. Thisdeposition is obtained by using conformal deposition techniques, forexample by CVD.

An example of steps of production of cap 6 will now be described on thebasis of a substrate 38 which is polished on both faces, for examplemade of silicon, glass, quartz, etc., designated cap substrate 38.

Firstly, marks (not represented) are defined and then etched in rearface 38.1 and in front face 38.2 of the substrate, these marks beingused for alignment between the NEMS substrate and the cap when they aresealed.

In a subsequent step a deposition of a hard mask, for example a siliconoxide mask several μm thick, is made on front face 38.2 of substrate 38(FIG. 20A). A photolithograph and etching of mask 40 take place todefine the cavities.

Cap substrate 38 is then etched, for example by DRIE (Deep ReactiveIonic Etching) with, for example, a method of the “Bosch” type,consisting in a succession of etching steps with a SF₆ plasma and ofpassivation with a C₄F₈ plasma, by this means forming the cavities whichwill delimit the fluid channels. The depth of the etching is, forexample, of the order of several hundred μm.

The hard mask can then be removed, for example by wet etching of the HFtype.

The element obtained in this manner is represented in FIG. 20B.

Two steps of lithography can then be accomplished if it is desired toobtain several etching depths, for example a first depth for the fluidchannel and a second depth to produce the inlet(s) or outlet(s) of thefluid channel.

As with the NEMS, the fluid channel can be functionalised by depositingmaterials on the inner faces of the etching made in the cap; thematerials can be those of the functionalisation layer of the NEMSstructure, or other materials.

We shall now describe a preferential example of assembly of the cap onthe substrate, by a dry resin film. In a preferred manner, and as willbe described, the dry film is formed on the cap.

In a subsequent step, cap 6 is prepared for sealing on the NEMS/MEMSstructure by means of a dry film. The cap's sealing surface is preparedso as to provide satisfactory adherence of the dry film on the cap.

Dry film 22 is then attached to front face 38.2 of cap substrate 38,this attachment advantageously being obtained by lamination. Thislamination enables the technique to be used despite the strong topologydue to the existence of the fluid channels on this side of thesubstrate.

In a subsequent step lithography and development are accomplished tostructure the dry film, and the latter then has beads along the cavitiesetched in the cap. This may be a broad bead, or alternatively, andpreferably, several narrow beads which are parallel to one another, asis represented in FIG. 20C. In this latter case, for example, the beadsand the spaces between the beads can measure between several μm andseveral tens of micrometers.

The beads preferably have a regular structure and a close sealingsurface over the entire structure to be sealed, to ensure uniformcrushing of the dry film with a reasonable pressure in the sealing step.

The element obtained in this manner is represented in FIG. 20C, and capsubstrate 38 is then ready to be sealed on to the substrate of NEMS/MEMSstructure 4.

As a variant, as was described above, other sealing techniques can beused to assemble the cap and the substrate. In this case otherpreparatory steps can be implemented, for example special cleaningsteps. Sealing techniques known to those skilled in the art cansubsequently be implemented, such as for example molecular sealing oragain eutectic sealing techniques, or metal sealing techniques, forexample by thermocompression, where some of these sealing techniques canrequire the prior formation of metal beads.

In a subsequent step, cap 6 and substrate 4 comprising the NEMS/MEMSstructure are sealed. Sealing is accomplished using sealing equipmentwhich enables the temperature and pressure applied between the cap andthe substrate to be sealed to be controlled. Surface treatments known atthe state of the art may possibly be undertaken to optimise the adhesionenergy.

Substrate 4 and cap 6 are firstly aligned by means of the marks madepreviously on the substrates.

Pressure is then applied between substrate 4 and cap 6, and a certaintemperature is also applied.

The applied pressure is, for example, of the order of several kN toseveral tens of kN, and the temperature is, for example, between 100° C.and 200° C.

Substrate 4 and cap 6 are then assembled. The fluid channel is thenfluid-tight at the lateral edges. The element obtained in this manner isrepresented in FIG. 20D.

An assembly such as the one of FIG. 20D is typically produced fromcircular substrates used in the microelectronics field.

The steps of production of the vias will now be described.

Preferably, in a step the silicon substrate in the rear face is thinned,for example by grinding and subsequently by chemical-mechanicalpolishing. By thinning the substrate in the rear face the depth of thevias is advantageously limited and the operations to fill the cavitieswith the metal are facilitated.

The remaining thickness of the substrate is such that sufficientthickness is retained to preserve a non-embrittled assembly. Thesubstrate in the rear face advantageously has a remaining thickness ofthe order of 15 μm to 50 μm, for vias of several μm wide, for example 5μm. This width enables a high contact density to be provided. With formfactors of the order of 2 to 10 the via depths are then approximately 10to 50 μm. These dimensions at once allow a high via density and preservea thickness of the layer of the substrate remaining after thinning whichis sufficient for the area of the substrate forming the lower base ofthe fluid channel to resist the thinning operations.

The depth of the fluid channel can, for example, measure several tens ofμm to several hundreds of μm, typically 100 μm for a 100 μm width.

Very advantageously, the thinning step takes place after the step ofsealing of the cap and of the NEMS substrate, such that the cap acts asa “handle” in the operations to thin the NEMS substrate. By this meansit is possible to obtain sufficient thinning of the substrate to attainthe desired via densities whilst retaining sufficient mechanicalproperties.

As a variant, the thinning step can be accomplished by chemical etching,plasma etching, etc.

The element obtained in this manner is represented in FIG. 21A.

In a subsequent step a layer of dielectric material 42 is formed in therear face, which is for example several μm thick. layer 42 is, forexample, silicon oxide deposited by PECVD, for example. The purpose ofthis layer 42 is to isolate the vias from a redistribution portion, alsocalled the RDL (Redistribution Layer), which will be combined in asubsequent step, in order to connect the device with vias to an externalelectronic circuit. The element obtained in this manner is representedin FIG. 21B.

In a subsequent step the vias are produced in the thinned substrate.

To accomplish this layer 42 is structured, for example by lithographyand anisotropic etching, for example by CHF₃ plasma. Silicon substrate27 is then etched, for example by SF₆ plasma DRIE and C₄F₈ passivation,and sacrificial layer 28 is also etched, for example by CHF₃ plasma,with the etching stopped at NEMS layer 30. The holes formed in thismanner are designated 44.

In a preferred manner a first deep etching is undertaken stopping atoxide layer 28, and a fine etching is then undertaken to reach layer 30and prevent it being damaged.

The element obtained in this manner is represented in FIG. 21C.

As a variant, the etching stops at the contact contacts and/or theinterconnection lines (FIG. 21C′) in order to produce a metal/metalcontact between the via and the contact or the interconnection lineinstead of a metal/silicon contact; layer 30 will then also be etchedwhen the via is etched.

The resin is then removed.

The etching methods are chosen advantageously in order to preventsub-etching and scalloping effects along the walls.

The dimensions of the holes are, for example, of the order of 2 μm to 10μm wide and 10 μm to 100 μm deep. These dimensions allow steps ofetching, cleaning of the via bases, conformity of the filling materials,etc.

As a variant, the etching could be accomplished by laser drilling, butstopping at layer 30 can be more complex.

In a subsequent step a layer of electrically insulating material 46 isformed on the inner face of holes 44, for example by deposition, wherethe material advantageously has very satisfactory conformity, forexample it is an SiO₂ dielectric formed by SACVD (Sub-atmosphericChemical Vapour Deposition) measuring several hundreds of nm, to producethe lateral electrical insulation of holes 44.

Other electrically insulating materials can be used, for example othertypes of SiO₂ and other dielectrics, for example a polymer.

The element obtained in this manner is represented in FIG. 21D.

In FIG. 21D′ holes 144 are covered with a layer of electricallyinsulating material 146.

As a variant, the etching described in relation with FIG. 21B stops insacrificial layer 28, which reduces the risks of damage of the NEMSlayer, which is fine with regard to the thickness etched in thesubstrate. The electrically insulating layer is then deposited and theetching is resumed to reach NEMS layer 30.

A step of cleaning and of surface preparation at the via base then takesplace.

A barrier layer (not represented) is then formed at the base of the holeand on the side walls of the holes, for example made of TiN, Ti, Ta,TaN, etc., for example measuring several tens of 10 nm. This is, forexample, deposited by sputtering or CVD, etc.

In a subsequent step a seed layer is formed, for example made of copperby PVD and/or CDV and/or sputtering to prepare for the filling of thevia by a metal. This layer is, for example, between several tens of nmand several hundreds of nm thick.

In a subsequent step the holes are filled with an electricallyconductive material 48 so as to form vias. The electrically conductivematerial is preferably metallic, for example made of Cu, W, or stronglydoped polysilicon Si, for example.

Filling is accomplished, for example, by ECD (Electro ChemicalDeposition). Thermal annealing can then take place. Filling can also beaccomplished by CVD or PVD, where these techniques enable satisfactoryconformity of the filling to be ensured.

A step of chemical-mechanical polishing then takes place to planarisethe assembly and to remove the surplus Cu.

The element obtained in this manner is represented in FIG. 21E; theelectrically conductive material of the via is in contact with thesilicon of the NEMS; for example it is the Cu/Si or W/Si contact. InFIG. 21E′ conductive material 148 is in contact with the metal presentat the surface of the contact contact or of the interconnection line,for example it is the Cu/Cu or Cu/AlSi contact.

For example a distribution layer or RDL can be formed at the surfacewhere the vias emerge, for example by implementing the following steps:

For example, a fine layer 50 of SiN nitride is formed in the rear face,being, for example, of the order of 50 nm thick, together with an RDLinstallation oxide layer which is several hundreds of nm thick on layer50.

In a subsequent step a lithography on layer 52 and an etching of RDLoxide 52 take place, stopping at layer 52, so as to form lines 54 etchedin the RDL oxide.

In a subsequent step the resin is removed.

Elimination of the SiN in the etched lines 54 perpendicular to the viasthen takes place to attain the vias. The lines are then cleaned.

In a subsequent step metallisation of the bottom of the lines takesplace, for example with a layer of TiN and copper. This metallisationis, for example, accomplished by PVD over a depth of several hundreds ofnm; the lines are then filled with copper 56, deposited for example byECD, for example over a thickness of 1 μm. Annealing andmechanical-chemical polishing then take place.

The element obtained in this manner is represented in FIG. 21F.

The RDL layer enables the TSV contacts to be distributed, and the deviceto be prepared for the connections with the exterior, for example withan integrated circuit. In addition, this layer can enable electricaltests to be accomplished to sort the dies, if required, beforeassembling them with the integrated circuit, which enables the costs tobe optimised while taking account of the productivity aspects, if theseare different for the devices of the invention and the integratedcircuits.

Alternatively the device can be prepared in a known manner for aconnection with integrated circuits (dies or wafers).

By this means operations to connect the devices to integrated circuitscan be accomplished by means of operations of the die transfer or wafertransfer type, by connecting the vias of the device of the invention toone of the metal levels of the integrated circuit(s), advantageouslythrough the RDL layer.

This operation can be accomplished in different ways by transferring onewafer to another wafer (“Wafer to Wafer”), or alternatively dies to awafer (“Die to Wafer”) or alternatively dies to dies (“Die to Die”). Inthe case of a die transfer the dies forming the integrated circuit canbe transferred to dies or wafers of devices of the invention, oralternatively vice versa.

The various techniques developed for 3D technologies in particular areconceivable, such as fusible balls, Au—Au sealings, polymer sealingswith metal patterns in a damascene configuration, etc.

These techniques can require that preparatory operations areaccomplished on the device of the invention and/or on the integratedcircuit portion, for example:

-   -   by undertaking particular operations to clean the metal layers,        for example for direct Cu—Cu sealings    -   by forming an RDL layer, as described above    -   by forming metal patterns (e.g. “Copper Pillar” for a Cu—Cu        sealing) at the surface of the device before applying        metal-metal sealing techniques such as Cu, Au, etc., sealing        techniques with fusible material such as InAu, CuSn, etc.),        sealing techniques with eutectic conductors, etc.    -   by forming fusible beads to apply flip-chip, AuSn, etc.        techniques.

In the method which has been described above, an intermediate layer 20was produced on the substrate comprising the NEMS before sealing to thecap.

But the device according to the invention cannot comprise anintermediate layer. In FIGS. 22A to 22E the steps of production of thevias in a device without an intermediate layer can be seen.

The steps of production of the substrate comprising the NEMS are similarto the steps represented in FIGS. 19A and 19B. In this example there isno production of interconnection lines.

The steps of production of the cap are similar to the steps representedin FIGS. 20A and 20B.

Sealing is accomplished in similar manner to the sealing of the steprepresented in FIG. 20C. This is preferably a dry film sealing, butalternatively it may be a eutectic sealing, a molecular sealing, a metalsealing by thermocompression, etc.

Production of the vias will now be described.

Production of the vias is similar to that of the steps represented inFIGS. 21C to 21E.

Firstly substrate 4 is thinned in its rear face, for example by grindingfollowed by CMP, in order to attain a thickness, for example, of between15 μm and 50 μm.

In a subsequent step a layer 57 of a dielectric material is formed inthe rear face.

The element obtained in this manner is represented in FIG. 22A.

In a subsequent step holes 58 are etched in the substrate using themethod described in relation with FIG. 21C. Etching can stop at NEMSlayer 30.

In a subsequent step a layer made of electrically insulating material60, for example SiO₂ SACVD, is deposited on the inner face of the holes,using the method described in relation with FIG. 21D.

The element obtained in this manner is represented in FIG. 22B.

In a subsequent step the vias are formed by filling the holes with anelectrically conductive material 62, preferably a metal, according tothe method described in relation with FIG. 21E.

The element obtained in this manner is represented in FIG. 22C.

We shall now describe a method of producing a device comprising anintermediate layer but with no interconnection line in the fluidchannel.

The first steps of production of the NEMS substrate are similar to thesteps of FIGS. 19A and 19B.

In a subsequent step an intermediate layer 20 is formed on layer 30. Itcan be formed from several materials, for example it can comprise at thesurface a layer which resists the etching to release the NEMS; forexample it can be made of amorphous silicon, which resists hydrofluoricacid vapour.

The element obtained in this manner is represented in FIG. 23A.

In a subsequent step intermediate layer 20 is structured so as toprovide access to the area where the NEMS structure(s) to be releasedis/are located. To do so a lithography and an etching of intermediatelayer 20 take place. In this example intermediate layer 20 is kept inthe assembly area. It could be structured in another way, as wasdescribed above, for example only above the sensitive portions,protecting the remainder of the surface, or alternative by etching inthe area of the assembly interface to remove the intermediate layer inthis area and keep only the fluid channel. The NEMS structure is thenreleased, example using hydrofluoric acid vapour.

The element obtained in this manner is represented in FIG. 23C.

The steps of production of the cap are similar to the steps representedin FIGS. 20A and 20B.

Sealing is accomplished in similar manner to the sealing of the steprepresented in FIG. 20C. This is preferably a dry film sealing, butalternatively it may be a eutectic sealing, a molecular sealing, asealing by thermocompression, etc.

In this embodiment the sealing is made between intermediate layer 20 andcap 6. The element obtained in this manner is represented in FIG. 23D.

Production of the vias will now be described.

Production of the vias is similar to that of the steps represented inFIGS. 21B to 21E.

Firstly substrate 4 is thinned in its rear face, for example by grindingfollowed by CMP, in order to attain a thickness, for example, of between15 μm and 50 μm.

In a subsequent step a layer 62 of a dielectric material is formed inthe rear face.

In a subsequent step holes 64 are etched in the substrate using themethod described in relation with FIG. 21C. The etching can stop at NEMSlayer 30 (FIG. 23E), or in sacrificial layer 28.

In a subsequent step a layer made of electrically insulating material66, for example SiO₂ SACVD, is deposited on the inner face of the holes,using the method described in relation with FIG. 21D.

In a subsequent step the vias are formed by filling the holes with anelectrically conductive material 38, preferably a metal.

The element obtained in this manner is represented in FIG. 23F.

In the examples of methods described above the vias are produced afterthe cap is sealed on to the NEMS substrate and after the NEMS arereleased. But the devices according to the invention could be producedusing methods in which the vias would be produced before releasing theNEMS and before sealing the cap on to the NEMS substrate, or afterreleasing the NEMS and before sealing it between the cap and the NEMSsubstrate.

As was mentioned above, devices can be manufactured collectively onsubstrates, for example made of silicon, where the formed assemblycomprises several parallel channels. The devices are then separated bycleavage and/or sawing operations, for example. It is desired to divideeach channel to form several devices, and to separate the channels fromone another.

It is desirable that the fluid channels are not contaminated during theseparation steps. To accomplish this, and very advantageously, firstlypartial cutting lines are made in the area of the inlets and outlets ofthe fluid channels, deep within the NEMS substrates and Cap orthogonalto the axis of the fluid channels, but which do not reach thesechannels, where the cutting lines then define planes perpendicular tothe axis of the channel; a cleavage operation then takes place whichallows final separation of the devices along the planes defined by thecutting lines.

It should be noted that the planes are secant with the axis of thechannel, but are not necessarily perpendicular to this axis.

With regard to separation in the directions parallel to the fluidchannels, conventional sawing operations can be used.

Depending on the approaches chosen in the case of a connection of thedevices with integrated circuits (WTW, DTW, DTD), the steps ofseparation of the dies of devices will be able to be undertaken beforeor after sealing with the integrated circuits.

By virtue of the invention a device can be produced with a fluid channelcomprising one or more mechanical structures suspended in the channel,by this means preventing the formation of vias in the cap and/or at thesealing interface and lateral interconnection lines, making productionof the tightness between the cap and the NEMS substrate more complex.

In addition, the invention enables networks of mechanical structures tobe produced easily, by allowing a dense and complex electricalinterconnection as close as possible to the mechanical structures with,possibly, several metal levels. The invention can also enable all thestructures and layers present in the channel to be encapsulated, exceptfor the sensitive structures with an encapsulation layer. Finally, itallows functionalisation to be implemented in the course of a method onsuspended mechanical structures.

The invention claimed is:
 1. A device comprising: a substrate comprisingat least one electronic structure including at least one of amicroelectronic structure and a nanoelectronic structure comprising atleast one sensitive portion, a cap, said cap being assembled with thesubstrate at an assembly interface, one fluid channel defined betweensaid substrate and said cap, said fluid channel comprising at least twoapertures to provide a flow in said channel, said electronic structurebeing located within the fluid channel, at least one electricalconnection between said electronic structure and the exterior of thefluid channel, the at least one electrical connection being formed by avia made at least partly through the substrate directly below theelectronic structure, and in electrical contact with the electronicstructure, and an intermediate layer located only at the assemblyinterface located between the cap and the substrate.
 2. A devicecomprising: a substrate comprising at least one electronic structureincluding at least one of a microelectronic structure and ananoelectronic structure comprising at least one sensitive portion, acap, said cap being assembled with the substrate at an assemblyinterface, one fluid channel defined between said substrate and saidcap, said fluid channel comprising at least two apertures to provide aflow in said channel, said electronic structure being located within thefluid channel, at least one electrical connection between saidelectronic structure and the exterior of the fluid channel, the at leastone electrical connection being formed by a via made at least partlythrough the substrate directly below the electronic structure, and inelectrical contact with the electronic structure, and an intermediatelayer located at least partly in the fluid channel, said intermediatelayer covering, in the fluid channel, at least partly the electronicstructure, except for the sensitive portion thereof.
 3. The deviceaccording to claim 2, in which the intermediate layer is anencapsulation layer.
 4. The device according to claim 2, in which thevia is in electrical contact with the electronic structure through acontact located in the fluid channel.
 5. The device according to claim2, in which the intermediate layer comprises an electrically insulatingmaterial.
 6. The device according to claim 2, comprising afunctionalization layer at least partly covering a part of the sensitiveportion of the electronic structure.
 7. The device according to claim 2,comprising several microelectronic or nanoelectronic structuresinterconnected in said fluid channel.
 8. The device according to claim7, in which the microelectronic or nanoelectronic structures areinterconnected by interconnection lines positioned in the fluid channel.9. The device according to claim 8, in which the intermediate layercomprises an electrically insulating material which electricallyinsulates the interconnection lines.
 10. The device according to claim2, comprising a dry sealing film interposed between the substrate andthe cap.
 11. The device according to claim 10, in which the dry sealingfilm comprises several beads.
 12. The device according to claim 2,comprising at least one layer of material interposed between thesubstrate and the cap making a eutectic or metallic sealing, orthermocompression sealing, or screen print sealing, or in which thesealing is a molecular sealing or glass frit.
 13. The device accordingto claim 2, in which the intermediate layer comprises at least a firstplanarizing layer and a second layer deposited on the first layer, saidsecond layer being made of a material sensitive to a step of release ofthe electronic structure.
 14. The device according to claim 2, in whichthe channel forms a gas chromatography microcolumn.
 15. The deviceaccording to claim 2, in which the intermediate layer comprises at leasta first planarizing layer and a second layer deposited on the firstlayer, said second layer being made of a material insensitive to a stepof release of the electronic structure.